The present invention relates in general to the treatment of selenium alloy particles prior to vapor deposition of the selenium alloy on a substrate and using the treated selenium alloy particles in a process to vapor deposit a selenium alloy layer onto a substrate to form electrophotographic imaging members. One embodiment of the present invention is directed to a process which comprises (1) heating particles of an alloy of selenium and an alloying component selected from the group consisting of tellurium, arsenic, and mixtures thereof while said particles are exposed to oxygen; (2) exposing the particles to water; and (3) subjecting the particles previously exposed to oxygen and water to a vacuum. Another embodiment of the present invention is directed to a process which comprises (1) providing particles of an alloy of selenium and an alloying component selected from the group consisting of tellurium, arsenic, and mixtures thereof; (2) forming selenium oxide on the surfaces of the particles; (3) converting the selenium oxide on the particle surfaces to selenious acid; and (4) removing the selenious acid from the particle surfaces. The present invention enables reduced fractionation of selenium and other alloying components during vacuum evaporation of selenium alloy particles that have been subjected to the process.
The formation and development of images on the imaging surfaces of electrophotographic imaging members by electrostatic means is well known. One of the most widely used processes is xerography, described in, for example, U.S. Pat. No. 2,297,691 to Chester Carlson. Numerous different types of electrophotographic imaging members for xerography, i.e. photoreceptors, can be used in the electrophotographic imaging process. Such electrophotographic imaging members can include inorganic materials, organic materials, and mixtures thereof. Electrophotographic imaging members can comprise contiguous layers in which at least one of the layers performs a charge generation function and another layer forms a charge carrier transport function, or can comprise a single layer which performs both the generation and transport functions. These electrophotographic imaging members can also be coated with a protective overcoating to improve wear.
Electrophotographic imaging members based on amorphous selenium have been modified to improve panchromatic response, increase speed and to improve color copyability. These devices are typically based on alloys of selenium with tellurium and/or arsenic. The selenium electrophotographic imaging members can be fabricated as single layer devices comprising a selenium-tellurium, selenium-arsenic, or selenium-tellurium-arsenic alloy layer which performs both charge generation and charge transport functions. The selenium electrophotographic imaging members can also comprise multiple layers such as, for example, a selenium alloy transport layer and a contiguous selenium alloy generator layer.
A common technique for manufacturing photoreceptor plates involves vacuum deposition of a selenium alloy to form an electrophotographic imaging layer on a substrate. Tellurium is incorporated as an additive for the purpose of enhancing the spectral sensitivity of the photoconductor. Arsenic is incorporated as an additive for the purpose of improving wear characteristics, passivating against crystallization, and improving electricals. Typically, the tellurium addition is incorporated as a thin selenium-tellurium alloy layer deposited over a selenium alloy base layer in order to achieve the benefits of the photogeneration characteristics of SeTe with the beneficial transport characteristics of SeAs alloys. Fractionation of the tellurium and/or arsenic composition during evaporation results in a concentration gradient in the deposited selenium alloy layer during vacuum evaporation. Thus, the term "fractionation" is used to describe inhomogeneities in the stoichiometry of vacuum deposited alloy thin films. Fractionation occurs as a result of differences in the partial vapor pressure of the molecular species present over the solid and liquid phases of binary, tenary and other multicomponent alloys. Alloy fractionation is a generic problem with chalcogenide alloys. A key element in the fabrication of doped photoreceptors is the control of fractionation of alloy components such as tellurium and/or arsenic during the evaporation of selenium alloy layers. Tellurium and/or arsenic fractionation control is particularly important because the local tellurium and/or arsenic concentration at the extreme top surface of the structure, denoted as top surface tellurium (TST) or top surface arsenic (TSA), directly affects xerographic sensitivity, charge acceptance, dark discharge, copy quality, photoreceptor wear and crystallization resistance. In single layer low arsenic selenium alloy photoreceptors, arsenic enrichment at the top surface due to fractionation can also cause severe reticulation of the evaporated film. In two layer or multilayer photoreceptors where low arsenic alloys may be incorporated as a base or transport layer, arsenic enrichment at the interface with the layer above can lead to severe residual cycle up problems. In single layer tellurium selenium alloy photoreceptors, tellurium enrichment at the top surface due to fractionation can cause undue sensitivity enhancement, poor charge acceptance and enhancement of dark discharge. In two layer or multilayer photoreceptors where tellurium alloys may be incorporated as a generator layer, tellurium enrichment at the upper surface of the tellurium alloy layer can result in similar undue sensitivity enhancement, poor charge acceptance, and enhancement of dark discharge.
One method of preparing selenium alloys for evaporation is to grind selenium alloy shot (beads) and compress the ground material into pellet agglomerates, typically 150 to 300 milligrams in weight and having an average diameter of about 6 millimeters (6,000 microns). The pellets are evaporated from crucibles in a vacuum coater using a time/temperature crucible designed to minimize the fractionation of the alloy during evaporation.
One shortcoming of a vacuum deposited selenium-tellurium alloy layer in a photoreceptor structure is the propensity of the selenium-tellurium alloy at the surface of the layer to crystallize under thermal exposure in machine service. To retard premature crystallization and extend photoreceptor life, the addition of up to about 5 percent arsenic to the selenium-tellurium alloy has been found beneficial without impairment of xerographic performance. It was found that the addition of arsenic to the composition employed to prepare the pellet impaired the capability of the process to control tellurium fractionation. Selenium-tellurium-arsenic pellets produced by the pelletizing process exhibited a wider variability of top surface tellurium concentrations compared to selenium-tellurium pellets. This wider variability of top surface tellurium concentrations was manifested by a correspondingly wider distribution of photoreceptor sensitivity values than the top surface tellurium concentration variations in the selenium-tellurium alloy pellets. In an extended photoreceptor fabrication run, up to 50 percent of the selenium-tellurium-arsenic pellets were rejected for forming high top surface tellurium concentrations which caused excessive sensitivity in the final photoreceptor.
In deposited layers of alloys of Se-Te, the normal percentages of top surface tellurium can cause excessively high photosensitivity. This photosensitivity is variable and changes as the surface of the layer wears away. Surface injection of corona deposited charge and thermally enhanced bulk dark decay involving carrier generation cause the toner images in the final copies to exhibit a washed out, low density appearance. Excessive dark decay causes loss of high density in solid areas of toner images and general loss of image density.
In three layered photoreceptors containing, for example, a base layer of selenium doped with arsenic and chlorine, a generator layer of selenium doped with tellurium and a top layer of selenium doped with arsenic, there is a susceptibility to changes in the Te concentration profile through the thickness of the Se-Te alloy layer due to Te diffusion. The diffusion rate is a function of the concentration of Te. Higher concentrations of Te diffuse at a higher rate. Such diffusion causes changes in the electrical properties as the concentration of Te changes. The diffusion occurs from the middle layer into the adjacent layers. Diffusion is a greater problem in alloys of Se-Te compared to alloys of Se-Te-As because some crosslinking occurs in the latter alloy.
For alloys of Se-As, a sufficiently high concentration of top surface arsenic causes reticulation of the surface of the deposited alloy layer. This occurs as the deposited surface cools down and the differential thermal contraction through the thickness of the layer causes the surface to wrinkle. The deposited layer also exhibits electrical instability with excessive dark decay under certain conditions. When the photoreceptor comprises a single layer Se-As alloy, about 1 to about 2.5 percent by weight arsenic, based on the weight of the entire layer, at the surface of an alloy layer provides protection against surface crystallization. When the concentration of arsenic is greater than about 2.5 percent by weight, reticulation or electrical instability risks become higher. However, the shift in photosensitivity is not large.
In the past, shutters have been used over crucibles to control fractionation. These shutters are closed near the end of the evaporation cycle. The tellurium or arsenic rich material arising from the crucible deposits on the shutter rather than on the photoreceptor. However, in planetary coating systems, installation of shutters is complex, difficult and expensive. Further, after one or more coating runs, it is necessary to clean the surface of the shutters and the resulting debris can cause defects to occur in subsequently formed photoreceptor layers.
Thus, a significant problem encountered in the fabrication of selenium alloy photoreceptors is the fractionation or preferential evaporation of a species such that the resulting film composition does not replicate the original composition. In other words, the deposited film or layer does not have a uniform composition extending from one surface to the other. For example, when tellurium is the dopant, the tellurium concentration is unduly high at the top surface and approaches zero at the bottom of the vacuum deposited layer. This problem is also observed for alloys of Se-Te, Se-As, Se-As-Te, Se-As-Te-Cl, and the like and mixtures thereof.
U.S. Pat. No. 4,780,386 (Hordon et al.), the disclosure of which is totally incorporated herein by reference, discloses a process in which the surfaces of large particles of an alloy comprising selenium, tellurium and arsenic having an average particle size of at least 300 microns and an average weight of less than about 1,000 milligrams are mechanically abraded while maintaining the substantial surface integrity of the large particles to form between about 3 percent by weight to about 20 percent by weight dust particles of the alloy based on the total weight of the alloy prior to mechanical abrasion. The alloy dust particles are substantially uniformly compacted around the outer periphery of the large particles of the alloy. The large particles of the alloy may be beads of the alloy having an average particle size of between about 300 microns and about 3,000 microns or pellets having an average weight between about 50 milligrams and about 1,000 milligrams, the pellets comprising compressed finely ground particles of the alloy having an average particle size of less than about 200 microns prior to compression. In one preferred embodiment, the process comprises mechanically abrading the surfaces of beads of an alloy comprising selenium, tellurium and arsenic having an average particle size of between about 300 microns and about 3,000 microns while maintaining the substantial surface integrity of the beads to form a minor amount of dust particles of the alloy, grinding the beads and the dust particles to form finely ground particles of the alloy, and compressing the ground particles into pellets having an average weight between about 50 milligrams and about 1,000 milligrams. In another embodiment, mechanical abrasion of the surface of the pellets after the pelletizing step may be substituted for mechanical abrasion of the beads. The process includes providing beads of an alloy comprising selenium, tellurium and arsenic having an average particle size of between about 300 microns and about 3,000 microns, grinding the beads to form finely ground particles of the alloy having an average particle size of less than about 200 microns, compressing the ground particles into pellets having an average weight between about 50 milligrams and about 1,000 milligrams, and mechanically abrading the surface of the pellets to form alloy dust particles while maintaining the substantial surface integrity of the pellets. If desired, the process may include both the steps of mechanically abrading the surface of the beads and mechanically abrading the surface of the pellets. The selenium-tellurium-arsenic alloy in the pellets may then be vacuum deposited to form a photoconductive layer of an electrophotographic imaging member which comprises a substrate and, optionally, one or more other layers.
U.S. Pat. No. 4,822,712 (Foley et al.), the disclosure of which is totally incorporated herein by reference, discloses a process for controlling fractionation by crystallizing particles of an alloy of selenium which comprises providing particles of an alloy comprising amorphous selenium and an alloying component selected from the group consisting of tellurium, arsenic, and mixtures thereof, said particles having an average size of at least about 300 micrometers and an average weight of less than about 1,000 milligrams, forming crystal nucleation sites on at least the surface of the particles while maintaining the substantial integrity of the particles, heating the particles to at least a first temperature between about 50.degree. C. and about 80.degree. C. for at least about 30 minutes to form a thin, substantially continuous layer of crystalline material at the surface of the particles while maintaining the core of selenium alloy in the particles in an amorphous state, and rapidly heating the particles to at least a second temperature below the softening temperature of the particles, the second temperature being at least 20.degree. C. higher than the first temperature and between about 85.degree. C. and about 130.degree. C. to crystallize at least about 5 percent by weight of the amorphous core of selenium alloy in the particles.
U.S. Pat. No. 4,842,973 (Badesha et al.), the disclosure of which is totally incorporated herein by reference, discloses a process for fabricating an electrophotographic imaging member which comprises providing in a vacuum chamber at least one crucible containing particles of an alloy comprising selenium and an alloying component selected from the group consisting of tellurium, arsenic, and mixtures thereof, providing a substrate in the vacuum chamber, applying a partial vacuum to the vacuum chamber, and rapidly heating the crucible to a temperature between about 250.degree. C. and 450.degree. C. to deposit a thin continuous selenium alloy layer on the substrate. A plurality of selenium containing layers can be formed by providing in the vacuum chamber at least one first layer crucible containing particles of selenium or a selenium alloy, at least one second layer crucible containing particles of an alloy comprising selenium, and a substrate, applying a partial vacuum to the vacuum chamber, heating the particles in the first layer crucible to deposit a thin continuous selenium or selenium alloy first layer on the substrate, maintaining the particles in the second layer crucible at a first temperature below about 130.degree. C. while the thin continuous selenium or selenium alloy first layer is being deposited on the substrate, and rapidly heating the particles in the second layer crucible to a second temperature between about 250.degree. C. and about 450.degree. C. to deposit a thin continuous selenium alloy second layer on the substrate.
U.S. Pat. No. 4,894,307 (Badesha et al.), the disclosure of which is totally incorporated herein by reference, discloses a process which comprises providing a chalcogenide alloy source material, crystallizing the source material, vacuum evaporating the source material, and adding in effective amounts thereto, prior to, during, or subsequent to evaporation, organic components such as siloxane polymers or greases, enabling the formation of a photoconductor with improved characteristics.
U.S. Pat. No. 4,859,411 (Sweatman et al.), the disclosure of which is totally incorporated herein by reference, discloses a process for crystallizing particles of an alloy of selenium which comprises providing pellets of an alloy comprising amorphous selenium and an alloying component selected from the group consisting of tellurium, arsenic, and mixtures thereof, said pellets having an average weight between about 50 milligrams and about 1,000 milligrams, exposing the pellets to an ambient temperature of between about 114.degree. C. and about 190.degree. C. until an exotherm occurs in the pellets at between about 104.degree. C. and about 180.degree. C., carrying the exotherm through to substantial completion, grinding the pellets into fresh powder having an average particle size of less than about 200 micrometers, and compressing the fresh powder into fresh pellets having an average weight between about 50 milligrams and about 1,000 milligrams.
U.S. Pat. No. 4,205,098 (Kobayashi et al.), the disclosure of which is totally incorporated herein by reference, discloses a process in which a powdery material of selenium alone or at least with one additive is compacted under pressure to produce tablets, the tablets being degassed by heating the tablets at an elevated temperature below the melting point of the metallic selenium and thereafter using the tablets as a source for vacuum deposition. The tablets formed by compacting the powdery selenium under pressure may be sintered at a temperature between about 100.degree. C. and about 220.degree. C. Typical examples of sintering conditions include 210.degree. C. for between about 20 minutes and about 1 hour and about 1 to about 4 hours at 100.degree. C. depending upon compression pressure. Additives mentioned include Te, As, Sb, Bi, Fe, Tl, S, l, F, Cl, Br, B, Ge, PbSe, CuO, Cd, Pb, BiCl.sub.3, SbS.sub.3, Bi.sub.2, S.sub.3, Zn, CdS2, SeS and the like. In one example, tablets having a thickness of 2 mm and a diameter of 6 mm were sintered and degassed at about 210.degree. C. for about 18 minutes.
U.S. Pat. No. 4,609,605 (Lees et al.), the disclosure of which is totally incorporated herein by reference, discloses a multilayered electrophotographic imaging member in which one of the layers may comprise a selenium-tellurium-arsenic alloy. The alloy can be prepared by grinding selenium-tellurium-arsenic alloy beads, with or without halogen doping, preparing pellets having an average diameter of about 6 mm from the ground material, and evaporating the pellets in crucibles in a vacuum coater.
U.S. Pat. No. 4,297,424 (Hewitt), the disclosure of which is totally incorporated herein by reference, discloses a process for preparing a photoreceptor wherein selenium-tellurium-arsenic alloy shot is ground, formed into pellets and vacuum evaporated.
U.S. Pat. No. 4,554,230 (Foley et al.), the disclosure of which is totally incorporated herein by reference, discloses a method for fabricating a photoreceptor wherein selenium-arsenic alloy beads are ground, formed into pellets and vacuum evaporated.
U.S. Pat. No. 4,205,098 (Kobayashi et al), the disclosure of which is totally incorporated herein by reference, discloses a method for producing selenium pellets wherein selenium or selenium and additives are formed into powder and then compacted into pellets and vacuum evaporated. The additives may include tellurium and arsenic.
U.S. Pat. No. 3,524,754 (Cerlon et al.), the disclosure of which is totally incorporated herein by reference, discloses a process for preparing a photoreceptor wherein selenium-arsenic-antimony alloys are ground into fine particles and vacuum evaporated.
U.S. Pat. No. 4,710,442 (Koelling et al.), the disclosure of which is totally incorporated herein by reference, discloses an arsenic-selenium photoreceptor wherein the concentration of arsenic increases from the bottom surface to the top surface of the photoreceptor such that the arsenic concentration is about 5 weight percent at a depth of about 5 to 10 microns on the top surface of the photoreceptor and is about 30 to 40 weight percent at the top surface of the photoreceptor. The photoreceptor is prepared by heating a mixture of selenium-arsenic alloys in a vacuum in a step-wise manner such that the alloys are consequentially deposited on the substrate to form a photoconductive film with an increasing concentration of arsenic from the substrate interface to the top surface of the photoreceptor. In one specific embodiment, a mixture of three selenium-arsenic alloys are maintained at an intermediate temperature in the range of from about 100.degree. to 130.degree. C. for a period of time sufficient to dry the mixture. The alloy may also contain a halogen. In Example X, the drying step temperature was attained in about 2 minutes and maintained for a period of approximately 3 minutes.
U.S. Pat. No. 4,583,608 (Field et al.), the disclosure of which is totally incorporated herein by reference, discloses heat treatment of single crystal superalloy particles. In one embodiment, single crystal particles are heat treated by using a heat treatment cycle during the initial stages of which incipient melting occurs within the particles being treated. During a subsequent step in heat treatment process substantial diffusion occurs in the particle. In a related embodiment, single crystal articles which have previously undergone incipient melting during a heat treatment process are prepared by a heat treatment process. In still another embodiment, a single crystal composition of various elements including chromium and nickel is treated to heating steps at various temperatures. In column 3, lines 40 to 47, a stepped treatment cycle is employed in which an alloy is heated to a temperature below about 25.degree. F. of an incipient melting temperature and held below the incipient melting temperature for a period of time sufficient to achieve a substantial amount of alloy homogenization.
U.S. Pat. No. 4,585,621 (Oda et al), the disclosure of which is totally incorporated herein by reference, discloses various selenium alloys, e.g., Se-Te and Se-As, containing phosphorous which are vacuum deposited on a substrate to form a photoreceptor.
U.S. Pat. No. 4,632,849 (Ogawa et al), the disclosure of which is totally incorporated herein by reference, discloses a method for making a fine powder of a metallic compound coated with ceramics. The process involves heating a gaseous mixture of at least methyl vapor and another element to a temperature not higher than 0.8 times as low as the melting point of the metal so that the metal and other element are reactive with each other while rapidly cooling to form a fine powder metallic compound. The metallic powder is further passed into another metal vapor to cover the metal powder with the other metal. The reaction system is cooled to a region in which the metal compound is kept stable to prevent further growth of the particles.
Swiss Patent Publication CH-656-486-A, published June 30, 1986, discloses production of PbTe, PbSn, PbSnTe, ZnTe, CdTe and CdHgTe by liquid phase epitaxy, the solvent for the telluride being a melt of arsenic telluride and/or antimony telluride.
Japanese Patent Publication J6 0172-346-A, published Sept. 5, 1985, discloses a process wherein TISe are placed in a crucible and heated at 180.degree. to 190.degree. C., Mg is added to the melting alloy, the temperature is raised to the 200.degree. to 220.degree. C. and allowed to stand at this temperature to form a uniform alloy of TIMgSe. The alloy is used in electric field-releasing ion beam generators.
U.S. Pat. No. 4,484,945 (Badesha et al.), the disclosure of which is totally incorporated herein by reference, discloses a process for preparing chalcogenide alloys by providing a solution mixture of oxides of the desired chalcogens and subsequently subjecting this mixture to a simultaneous coreduction reaction. Generally the reduction reaction is accomplished at relatively low temperature, not exceeding about 120.degree. C.
Japanese Patent Publication 57-1567 to Tokyo Shibaura Denki K.K., published June 7, 1982 discloses a process wherein an amorphous photoconductive material is obtained by combining selenium, arsenic, antimony and tellurium. This raises the glass transition point.
U.S. Pat. No. 4,414,179 (Robinette), the disclosure of which is totally incorporated herein by reference, discloses a process for preparing a selenium alloy comprising heating a mixture comprising selenium, arsenic and chlorine to a temperature between about 290.degree. C. and about 330.degree. C. to form a molten mixture, agitating the molten mixture to combine the components, continuing all agitation, raising the temperature of the mixture to at least 420.degree. C. for at least about 30 minutes and cooling the mixture until it becomes a solid. This alloy may be vacuum deposited.
U.S. Pat. No. 4,015,029 (Elchiasak), the disclosure of which is totally incorporated herein by reference, discloses a selenium alloy evaporation technique for depositing photoconductive material onto a substrate. The technique involves incorporating 1 to 80% by weight of at least one nonvolatile infra red absorbing heat sink in or within the body of inorganic photoconductive material and thereafter heating the resulting mixture with infra red heat.
U.S. Pat. No. 3,785,806 (Henrickson), the disclosure of which is totally incorporated herein by reference, discloses a process for producing arsenic doped selenium by mixing finely divided selenium with finely divided arsenic in an atomic ratio of 1:4 and thereafter heating the mixture in an inert atmosphere to obtain a master alloy. The master alloy is then mixed with molten pure selenium to attain an arsenic content of between 0.1 and 2% by weight based on the selenium.
U.S. Pat. No. 3,911,091 (Karem et al.), the disclosure of which is totally incorporated herein by reference, discloses a method for fabricating a photoreceptor by incorporating trigonal selenium particles in an organic binder material.
U.S. Pat. No. 4,513,031, the disclosure of which is totally incorporated herein by reference, discloses a process for the formation of an alloy layer on the surface of a substrate which comprises forming in a vessel a molten bath comprising at least one vaporizable alloy component having a higher vapor pressure than at least one other vaporizable alloy component in the bath, forming a thin substantially inert liquid layer of an evaporation retarding film on the upper surface of the molten bath, the liquid layer of the evaporation retarding film having a lower or comparable vapor pressure than both the vaporizable alloying component having a higher vapor pressure and the other vaporizable alloying component, covaporizing at least a portion of both the vaporizable alloying component having a higher vapor pressure and the other vaporizable alloying component whereby the evaporation retarding film retards the initial evaporation of the vaporizable alloying component having a higher vapor pressure, and forming an alloy layer comprising both the vaporizable alloying component having a higher vapor pressure and the other vaporizable alloying component on the substrate. Examples of vaporizable alloying components include selenium-sulfur and the like, and examples of vaporizable alloying components having relatively low vapor pressures which include tellurium, arsenic, antimony, bismuth, and the like. Examples of suitable evaporation retarding film materials include long chain hydrocarbon oils, inert oils, greases or waxes at room temperature which flow readily at less than the temperature of detectable deposition of the vaporizable alloying components having higher vapor pressures in the alloying mixture. Examples of retarding materials include lanolin, silicone oils such as dimethylpolysiloxane, branched or linear polyolefins such as polypropylene wax and polyalpha olefin oils, and the like. According to the teachings of this patent, optimum results are achieved with high molecular weight long chain hydrocarbon oils and greases generally refined by molecular distillation to have a low vapor pressure at the alloy deposition temperature.
U.S. Pat. No. 4,770,965 (W. Fender et al.) discloses a process which includes heating an alloy comprising selenium and from about 0.05 percent to about 2 percent by weight arsenic until from about 2 percent to about 90 percent by weight of the selenium in the alloy is crystallized, vacuum depositing the alloy on a substrate to form a vitreous photoconductive insulating layer having a thickness of between about 100 microns and about 400 microns containing between about 0.3 percent and about 2 percent by weight arsenic at the surface of the photoconductive insulating layer facing away from the conductive substrate, and heating the photoconductive insulating layer until only the selenium in the layer adjacent the substrate crystallizes to form a continuous substantially uniform crystalline layer having a thickness up to about one micrometer. A thin protective overcoating layer is applied on the photoconductive insulating layer. The selenium-arsenic alloy may be at least partially crystallized by placing the selenium alloy in shot form in a crucible in a vacuum coater and heating to between about 93.degree. C. (200.degree. F.) and about 177.degree. C. (350.degree. F.) for between about 20 minutes and about one hour to increase crystallinity and avoid reticulation. Preferably, the selenium-arsenic alloy material in shot form is heated until from about 2 percent to about 90 percent by weight of the selenium in the alloy is crystallized. The selenium-arsenic alloy material shot may be crystallized completely prior to vacuum deposition to ensure that a uniform starting point is employed. However, if desired, a completely amorphous alloy may be used as the starting material for vacuum deposition. In Examples II and V of this patent, halogen doped selenium-arsenic alloy shot contained about 0.35 percent by weight arsenic, about 11.5 parts per million by weight chlorine, and the remainder selenium, based on the total weight of the alloy was heat aged at 121.degree. C. (250.degree. F.) for 1 hour in crucibles in a vacuum coater to crystallize the selenium in the alloy. After crystallization, the selenium alloy was evaporated from chrome coated stainless steel crucibles at an evaporation temperature of between about 204.degree. C. (400.degree. F.) and about 288.degree. C. (550.degree. F.).
U.S. Pat. No. 4,904,559 (Badesha et al.) discloses a process for the preparation of chalcogenide alloy compositions which comprises providing a chalcogenide alloy, admixing therewith crystalline or amorphous selenium, and subsequently subjecting the resulting mixture to evaporation.
U.S. Pat. No. 5,030,477 (Badesha) discloses a process for the preparation of chalcogenide alloy compositions which comprises providing a chalcogenide alloy, admixing therewith a metal oxide, and subsequently subjecting the resulting mixture to evaporation.
U.S. Pat. No. 5,002,734 (Kowalczyk et al.), discloses a process for the preparation of chalcogenide alloys which comprises crystallizing a chalcogenide alloy source component, grinding and pelletizing the crystallized alloy product, and evaporating the alloy onto a supporting substrate.
Difficulties continue to be encountered in achieving precise control of tellurium and/or arsenic fractionation in the outer surface of a vacuum deposited photoconductive layer. This, in turn, affects the physical or electrical properties of the final photoreceptor. Photoreceptors containing large batch to batch top surface tellurium or arsenic concentrations tend to exhibit correspondingly large batch to batch variations in physical or electrical properties, which is unacceptable in high speed precision copiers, duplicators and printers because of copy quality variations. Moreover, variations in physical or electrical properties as a photoreceptor surface wears away during cycling is unacceptable in high speed precision copiers, duplicators, and printers, particularly during long length runs where, for example, the copy quality should be uniform from the first copy to thousands of copies. High speed copiers, duplicators and printers are constrained by narrow operating windows that require photoreceptors having precise, predictable operating characteristics from one batch to the next and during cycling.
Thus, there is a need for an improved process for preparing photoreceptors comprising selenium alloys containing additives such as tellurium and/or arsenic.